diff --git a/MEV_on_Ethereum/block_builders.md b/MEV_on_Ethereum/block_builders.md
index eb0f408..0a4442c 100644
--- a/MEV_on_Ethereum/block_builders.md
+++ b/MEV_on_Ethereum/block_builders.md
@@ -10,6 +10,7 @@
 
 ### resources
 
+* [ef builder specs](https://github.com/ethereum/builder-specs)
 * [flashbots builder](https://github.com/flashbots/builder)
 * [etherscan blocks](https://etherscan.io/blocks), [mev blocks](https://etherscan.io/blocks/label/mev-block), and [mev builders](https://etherscan.io/accounts/label/mev-builder)
 * [builder69.io endpoint for searchers (bundle/tx)](https://builder0x69.io)